Analysis of GIS Data by Simple Examination - Introducing Geographic Information Systems with ArcGIS - page 367

selected. The number of selected records is shown at the bottom of the table. Also at the
bottom of the table, you can choose whether the window displays all the records or only those
selected. Choose records with OBJECTIDs 2, 3, 5, 7, 11, 13, 17, 19, and 23. Show only
those selected records. Then show all records.
13. Use simple logic to select records: Press the Table Options button on the table window. Press
Switch Selection. Note that all records except 2, 3, 5, 7, 11, 13, 17, 19, and 23 are selected.
Now switch the selections in a different way: press the Switch Selection button on the table
menu bar. Choose Clear Selection, then Switch Selection, then Clear Selection. Find a way to
Select All, and finally, Clear Selection from the Table Options menu.
14. Select records by attributes: Click Table Options > Select By Attributes to bring up a window of
(almost) the same name. Type the following expression (observing capitalization) in the large
blank in this window:
[Shape_Length] <= 201
and click Apply. This selects all those records that have a Shape_Length value less than or
equal to 201. Dismiss the Select by Attributes window. Examine the table. Show only selected
records. How many selected records are there? _____ out of _____. Run Statistics on the
Shape_Length field. What is the average? ________. Now dismiss the Selection Statistics of
Landcover window, select Show All Records, and run Statistics again. What is the average?
________. Choose Clear Selection. Run Statistics again. What is the average? ________.
Make a note to yourself in your Fast Facts File that if any records are selected, no matter what
records are shown, statistics are calculated only on the selected records . Forgetting this fact is
a good way to get wrong answers. Dismiss the statistics window.
15. Again click Table Options > Select By Attributes. Erase the expression (there is a Clear button).
Experiment by building the partial expression
[Shape_Area] <=
by clicking or double-clicking various buttons and values in the window. This query-building
method is a quick way to create an expression while avoiding the possibilities of mistyping.
(Even when you use the query builder, you still can type parts of an expression, and at times
you may have to.)
Surrounding feature class names with square brackets (i.e., [and]) works with personal
geodatabases but not with file geodatabases, where double quotation marks are used instead.
(There are several other differences in syntax between the types of geodatabases. When you
want to see these differences, you can go to HELP, click the Search tab, type “Migrating to the
file geodatabase” into the text box, press the “ask” button, and then display Migrating to
the file geodatabase. For now, just put this in your Fast Facts File.)
Press Get Unique Values to bring up all the possible Shape_Area values in the Unique Values
pane. Scroll down to the value that begins 7710.087 and double-click. This will complete the
expression:
[Shape_Area] <= 7710.08730661013